This invention relates to magnetic sensor devices used in data storage systems. More particularly, the invention relates to oxidized metal insulator layers used in magnetic sensor devices.
Metal-oxide layers are used in laminated magnetic sensor devices as gap insulator layers to electrically isolate the magnetic sensing elements. For example, a typical magneto-resistive or spin-valve sensor device has a multi-layer magnetic sensor element integrated between two metal-oxide layers. The metal-oxide layers are surrounded by metallic magnetic shields, which define the operational width of the sensor device. The metal-oxide gap insulator layers that are laminated between the magnetic shields and the magnetic sensor element prevent shorting between the shields and sensor layers.
Magnetic sensor devices, similar to that described above, are usually made in a sequential deposition process, wherein each layer of the sensor device is deposited one after the other. For example, a magnetic shield layer, usually a NiFe alloy, is deposited on a suitable substrate. On the magnetic shield layer a first metal-oxide gap insulator layer is deposited followed by the formation of the multi-layer magnetic sensor element, the deposition of a second metal oxide gap insulator layer and deposition of a capping magnetic shield layer.
Metal-oxide gap insulator layers are commonly made of Al2O3 deposited reactively from atomized Al particles in an oxygen-containing environment, or deposited directly from Al2O3 sources by RF sputtering or ion-beam sputtering. A major shortcoming of metal-oxide gap insulator layers produced by this method is that the metal-oxide layers are required to be several hundred Angstroms thick in order be electrically insulating layers that are free from pinholes, through layer cracks or other defects that deteriorate their insulating properties. When the metal-oxide insulating gap layers have pinholes, through layer cracks or other defects, current leaks and electrical shorts will occur between a sensor element and the surrounding magnetic shields.
Because the gap insulator layers made by prior art methods are required to be relatively thick, they thermally insulate the integrated sensor element and prevent efficient dissipation of heat away from the sensor during operation of the device. Efficient dissipation of heat is required in order to operate a magnetic sensor device at high drive currents and improve the signal to noise ratio.
What is needed is a magnetic sensor device with a reduced gap thickness in order to increase the recording readback capabilities of the device for application with high areal densities. Further, there is a need for magnetic sensor devices that provide a mechanism to efficiently dissipate heat away from the sensor elements during read and write operations allowing for the use of higher drive currents to improve signal and reduce noise. There is also a need to provide an improved method for producing insulating gap layers of any thickness in laminated magnetic sensor devices
Accordingly, it is a primary object of the present invention to provide a magnetic sensor device that has a thin oxidized metal insulator layer positioned between a magneto-resistive sensor or spin-valve sensor structure and a magnetic shield. Oxidized metal insulator layers, herein refers to metal-oxide metal nitrides, metal-oxy-nitrides, metal-fluorides, and other reactively formed metal compounds. The thin oxidized metal layer allows for a reduction in the overall thickness of the sensor device and increases its areal density recording and readback capabilities of the device.
It is a further object of the present invention to provide a magnetic sensor device that has a thin oxidized metal layer/metal layer gap insulator substructure laminated between a sensor element and a magnetic shield with the oxidized metal layer in contact with the sensor structure. Because the oxidized metal layer is thin and in contact with the sensor structure, heat generated at the sensor structure during operation of the sensor device can be more efficiently transferred to the metal layer. The metal layer acts as a heat sink to dissipate and draw heat away from the sensor structure. The sensor device with a thin oxidized metal layer in contact with the sensor and a metal layer underlay provides for a magnetic sensor device that can operate at higher drive currents leading to improved signal to noise ratios during reading and recording operations.
It is also an object of the present invention to provide a laminated magnetic sensor device with a plurality of oxidized metal/metal gap substructures. The plurality of oxidized metal/metal gap substructures again helps to efficiently dissipate heat away from the sensor element and allows the device to operate at higher drive currents leading to improved signal to noise ratios.
It is yet another object of the present invention to provide a method for producing high quality oxidized metal gap insulator layers of any thickness in laminated magneto-resistive and spin-valve sensor devices. The method of the current invention is to produce high quality oxidized metal insulator gap layers in sensor devices and reduce failures that result from pinholes, through layer cracks or other defects.
The objects and advantages of the invention are achieved by providing a laminated magnetic sensor that has a magneto-resistive or spin-valve sensor element laminated between metal oxide insulating gap structures. At least one of the insulating gap structures contains an oxidized metal layer and/or an oxidized metal/metal underlay sub-structure, wherein the oxidized metal is formed by the oxidization, either partial or complete, of a previously deposited metal layer. For example, magnetic sensors of the current invention have gap structures that include oxidized metal layer/metal underlayer substructures of Al-oxide/Al, Ta-oxide/Ta, Co-oxide/Co, Fe-oxide/Fe, Ti-oxide/Ti, Ru-oxide/Ru, Si-oxide/Si, Cu-oxide/Cu, Ni-oxide/Ni, NiFe-oxide/NiFe or Cr-oxide/Cr.
Sensor devices according to the current invention, also have a plurality of oxidized metal layer/metal underlayer substructures within an insulating gap structure. Each one of the plurality of oxidized metal/metal substructures is made of the same oxidized metal/metal combination or different oxidized metal/metal combinations may be used for each of the substructures. Alternatively, a gap insulator structure may have substructures with a plurality of metal layers with one or more of the plurality of metal layers having a metal oxide-layer formed thereon, as described above.
The oxidized metal layer/metal underlayer substructures are formed by depositing a metal layer of Al, Ta, Co, Ti, Fa, Ru, Si, Cu, Ni, or Cr that is preferably 5 Angstroms thick or greater, so that it forms a continuous layer. The metal layer is subsequently oxidized to convert a portion of or all of the metal layer to the corresponding oxidized metal. In the case of an alloy metal layer, one of the components of the alloy may be preferentially oxidized to form the insulating layer. Oxidized metal layers produced by this method are typically very thin and thus provide for very little thermal insulation or afford good heat dissipation. However, because the oxidized metal layers are uniform in thickness and of high quality they are suitable dielectric separator layers in gap structures of magnetic sensing devices. Further, the remaining un-oxidized portion of the metal layer (the metal underlayer), if any, provides a conductive path for efficient dissipation of heat away from the sensor element, thus allowing the magnetic sensing devices of the current invention to operate at higher drive currents. Also, because oxidized metal layer/metal underlay substructures are thin the overall gap width of the device is reduced and the device can provide for higher areal data density access in a data storage system.
The method of the current invention is used to make oxidized metal gap insulator layers of any thickness. The gap insulator layers are metal oxides, metal nitrides and metal oxy-nitrides. In a particular embodiment of the invention an insulator gap structure is provided by oxidizing a portion of a metal layer to from a oxidized metal layer/metal underlayer substructure as previously described and in a subsequent step a thicker layer of oxidized metal is deposited thereon to any desired thickness.